1. Field of the Invention
The present invention relates to image display apparatus of the rear projection type having a projector device with a periodical pixel structure including, but not limited to, a liquid crystal display panel and also having a screen for permission of projection of images thereonto from the projector device.
2. Description of the Prior Art
Conventionally, as image projector devices adaptable for use in rear projection image display apparatus, xe2x80x9cthree-tubexe2x80x9d cathode-ray tube (CRT) devices have been widely employed which include three independent tubes for three fundamental colors, such as red (R), green (G) and blue (B). With such three-tube projector, relatively high luminance intensity or brightness is attainable. However, this does not come without accompanying a penaltyxe2x80x94the difficulty in meeting light-weight and small-size requirements. In recent years, specific rear projection image display apparatus which employs liquid crystal display panels, digital micro-mirror devices (referred to as the xe2x80x9cDMDsxe2x80x9d hereinafter) or equivalents thereto is under development in order to reduce the weight and dimension thereof.
In the image display apparatus utilizing the three-tube projector device, one typical screen for use in displaying images is configured from a couple of componentsxe2x80x94a Fresnel lens sheet, and a lenticular lens sheet as shown in FIG. 7. As shown herein, the lenticular lens sheet has its light incidence surface and light exit surface, on respective ones of which cylindrical or xe2x80x9clenticularxe2x80x9d lenses 21, 22 are formed each having a horizontally periodical surface configuration structure, while forming a light absorption layer 23 on selected part of the light exit surface which might be free from collection of light rays as introduced from the lens on the light incidence surface side. Typically, the pitch of lenticular lenses 21, 22 may be greater than or equal to 0.5 mm.
Currently available projector devices including, but not limited to, liquid crystal display panels and DMDs, are designed to have periodical pixel configuration in both the horizontal direction and the vertical direction. In cases where a projector device having such periodical pixel structure is used in combination with the prior known screen for use with three-tube projector devices, a problem of moire generation might arise due to the fact that each of the projector device and lenticular lenses of its associative screen has the horizontal periodic structure.
One approach to avoiding the moire problem has been disclosed, for example, in Published Unexamined Japanese Patent Application No. 2-97991, which is designed so that the ratio of lenticular lens pitch to the horizontal pitch of an image due to liquid crystal display panel pixels is selected to satisfy xe2x80x9c1/(N+xc2xd)xe2x80x9d where N is an integer greater than or equal to 1. According to the teachings, the value of such parameter xe2x80x9cNxe2x80x9d is typically set at 2 or greater. Supposing that the pitch of a pixel image as projected onto the screen is 1.0 mm, the pitch of lenticular lens satisfying the above formula may be as small as 0.4 mm if N is 2, 0.28 mm for N=3, and 0.222 mm for N=4. In recent years, as the pixel pitch decreases for achievement of demands for higher image display precision and resolution, the pitch of such lenticular lens decreases accordingly.
Use of certain screens designed causing the lenticular lens pitch to meet the ratio discussed above might enable avoidance of moire creation on display screens. Unfortunately, this still suffers from a problem of observability of an unwanted pattern of thin vertical lines on the display screen (such unwanted pattern of thin vertical lines will be referred to as the xe2x80x9cnon-uniform vertical linesxe2x80x9d hereinafter).
Incidentally, one prior known design scheme for numerical determination of the shape of the lenticular lens sheet shown in FIG. 7 has been disclosed for example in Published Unexamined Japanese Patent Application No. 58-221833. With this design scheme, the ratio (d/p1) of the pitch xe2x80x9cp1xe2x80x9d of lenticular lenses on the light incidence surface side to the thickness xe2x80x9cdxe2x80x9d of its associated lenticular lens sheet (the distance between one light incidence surface-side lenticular lens and its associative lenticular lens on the light exit surface side) may typically fall within a range of from 1.1 to 1.25 in order to obtain the horizontal-direction screen characteristics required. Accordingly, for purposes of elimination of onscreen moire generation, the need arises to decrease the sheet thickness so that it is as small as 0.44 to 0.5 mm in cases where the lenticular lens pitch p1 is set at 0.4 mm according to the design teachings discussed above.
While the lenticular lens sheet may generally be manufactured by use of optically transparent or light-transmissive thermal irreversible resin materials, a simple decrease in sheet thickness with a decrease in pitch of miniaturized lenticular lenses would result in an increase in difficulty of the manufacture thereof, while simultaneously decreasing the mechanical strength or stiffness of the resultant lenticular lens sheet.
It is therefore an object of the present invention to provide improved image display apparatus capable of avoiding the problems encountered with the prior art.
It is another object of the invention to provide image display apparatus with an associative projector device having horizontal pixel structures capable of eliminating, or at least greatly suppressing, occurrence of vertical linear on-screen noise patterns including non-uniform vertical lines.
It is another object of the invention to provide image display apparatus of the rear projection type employing a screen of enhanced physical strength.
To attain the foregoing objects the present invention provides specific rear projection image display apparatus which comprises: (1) a screen including a lenticular lens sheet having a light incidence surface with lenticular lens components being periodically provided thereon and a light exit surface having a substantially flat surface at or near the focal position of each lenticular lens on the light incident surface, and also having a light absorption layer provided in a region different from the focal position; and (2) a projector device of the periodical pixel configuration, including an array of pixels as periodically disposed thereon, for projecting images onto the screen.
In accordance with one aspect of the invention, it may be preferable that micro-lenticular lenses are provided on the substantially flat surface, which have a periodical pixel configuration that is similar in direction to that of the lenticular lenses on the light incidence surface, because of the capability of increasing horizontally diffused light rays. More specifically, the micro-lenticular lenses are such that the pitch may range from 0.03 to 0.1 mm and that the lens height falls within a range of from 0.003 to 0.03 mm. In view of the fact that the prior art lenticular lens sheets are typically designed so that the pitch of lenticular lenses ranges from 0.2 to 0.5 mm while the lens height is from 0.03 to 0.08 mm, the micro-lenticular lenses in the lenticular lens sheet of the invention may be clearly distinguishable in this respect over the prior art lenticular lenses on the light exit surface side thereof.